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PECT/F/ER VAR/ABLE T/PANSM/SS/ON FROM TO SUSTA/NED F/PEOUE/VCY AMPLIFIER@Mwmc/ fiaiaif United States, Patent METHOD AND APPARATUS FOR PRODUCINGSOUNDS Osmond Kendall, Ottawa, Ontario, Canada Application May 7, 1951,Serial No. 224,927

Claims priority, application Great Britain May 16, 1950 32 Claims. (Cl.179-1) This invention relates to a method and apparatus for producingsounds which may be auditioned or recorded as desired and isparticularly concerned with the produc tion of original recordings ofmusic which may be created directly in sound-track form without priorinstrumentation by musicians.

Prior to the present invention, musical expression has been limited bythe fixed characteristic tones inherent in a given acoustic musicalinstrument. It had to be accepted by the composer and the arranger of apiece of music that some musical instruments are inflexible in that theypossess a characteristic touch which is determined by their design. Thisrigid factor is a limitation thwarting the full freedom of musicproduction according to the concepts of a composer or arranger. It hasbeen proposed to overcome this difiiculty, which is inherent in musicoriginated by acoustic instruments, by hand-drawing sound waves andphotographing the hand-drawn sound waves to produce a sound track. Whiledirect production of a sound track by hand-drawing creates new musicalfreedom from the characteristic touch of instruments, it has never beenused to any great extent owing to it being painstaking and laborious.

The present invention provides a method and apparatus for producingsounds which provide musical freedom from the characetristic touch ofinstruments without the painstaking and laborious work of hand-drawingeach note.

The present invention takes cognizance of the theory that the quality ofa sound, such as a musical note, which makes it recognizable as beingoriginated by a particular musical instrument and even by a particularmusician, is a combination of some of the following components of music:

(a) A primary sustained audio frequency which may be a single frequencyor may include a series of harmonics. The relative amplitudes of any ofthese frequencies may vary from zero to one hundred percent of thefrequency of highest amplitude in the series, including the fundamentalfrequency. A number of different fundamental frequencies and theirrespective series of harmonics may concurrenlty comprise the basicsustained audio frequency.

(b) A shifting in frequency of the basic sustained audio frequency, asexemplified in slide string-instrument renditions, tremolo effects,clang percussive note advents and vibrato die-away eifects, etc.

(0) A progression of varying instant amplitudes which comprise theelement of tone in the rendition of a given note of music. Such anenvelope of sequential amplitudes does not have separable componentswhich differentiate between touc as provided by the nature andconstruction of the musical instrument, and touch which ischaracteristic of expression as played by the musician. The contour ofthe envelope may be further complicated by acoustic reverberation whichalso appears in part as a sequence of instant amplitude changes. In theplaying of a musical instrument the natural tone is 2,734,100 PatentedFeb. 7, 1956 'ice emitted at the selected frequency in a progression ofchanges of amplitudes as determined by the touch of the musician and bythe touch resulting from the construction of the instrument in question.This combined touc may be observed in timbrillated contour form on anoscilloscope.

(d) Duration and advent time expressed as physical lengths which areadjustable in the following sense: for example consider an envelope ofthe touch of a piano which rises rapidly to a maximum on the impact ofthe felt and may decay over a duration of six seconds depending on thenote selected. The characteristic but contracted contour of the envelopewill be similar in the case of a higher frequency note lasting onesecond. It will be apparent that the required envelope contour is notobtained by cutting off or deleting 5 seconds worth of the 6 secondcontour length. It will further be apparent that placement of the adventof a note on a given soundtrack is a convenient physical lengthequivalent of time relationship between notes of music which may be inrecording assembly.

According to the present invention an envelope contour, made inaccordance with the component of sound corresponding to a progression ofinstant amplitudes of sound, is used to control the audio frequencycurrent corresponding to the primary audio frequency component of soundso that the residue of the audio frequency current conforms to theenvelope contour. The residue of the audio frequency current may then berecorded according to given advent placements on the sound-track of arecording.

In accordance with the present invention the audio frequency currentcorresponding to the primary audio frequency component of sound forms amusical raw material which is characetristic of any actual or imaginarymusical instrument as desired by the composer. The audio frequencycurrent is deleted according to a desired envelope contour whichsupplies the touch component of music, leaving a residue of the audiofrequency current which can be recorded and rerecorded in accordancewith deliberated advent times as represented by linear distances along asound-track.

The present invention enables the producer of music to have a fullchoice of any characetristic tone and an independent but equally fullchoice of any characteristic touch, without restriction to the fixedcombinations of characteristics obtainable from selected musicalinstruments. According to the present invention the notes of a musicalcomposition do not have to be produced in,

any particular time sequence of notes, as is the case when music isproduced conventionally, and each note may be individually produced andtailored to the composers or the arrangers wishes before being mixedwith other notes of the composition.

A further important advantage resulting from the ability to producenotes individually without regard to any particular time sequence ofnotes is that synchroni- Zation of the music recorded on the sound-trackof a motion picture. film with the visual content of the film can beachieved. This synchronization is often desired by the composer andarranger but, prior to the present invention, it was usually notobtainable due to the difficulty of playing live music (that is, musicproduced acoustically by musicians) in a predetermined synchronizedrelation to the action recorded in the visual content of the film. Whenlive music is recorded on a soundtrack it may prove completely unusableshould even a small portion of it be undesirably executed, mislocated asto precise advent in time, incorrect in pitch relationship, undesirablycombined with acoustic reflections, or otherwise improperly performed.Perfection of the final recorded music by subdividing it into editablefragments of recordings of thecomponent music is precluded becausemusicians a n tiSFWFQIi YrsafOtm he. omp n nts.

of their art in a state of complete dissociation from musical contexts.Also, since the individual instrumcntations of an orchestration aremerged into a complex wave in a single medium, either air or therecording channel, it follows that the editing of an offendingcomponentof live music in a given rendition is impractical. Thus, prior to thepresent invention, it was either necessary to repeat the entirerecording or to accept a recording of a standard of performance belowthat which is possible.

In the present specification and claims the term soundtrack is usedtodenote a track on a medium adapted to receive a recordingof sound. Theterm wide' soundtraclc is used 'to denote a track on a. medium such asmagnetic tape, photographic film or the like; adapted to receive arecording invariable signal density form extending acrossawidthadaptedfor convenient manual erasure of portions of .therecordedvolume of .a signal.

The invention will befurther described with reference to theaccompanying drawings, in which:

Figure 1, isja perspective view of apparatus in ac cordance with anembodiment of. the invention;

Figure 2 is; schematic diagram of the apparatus shown in Figure 1;

Figure 3 is a schematic diagram of a preferred form of aperiodicpolyharmonic generator according to the invention, for use withtheapparatus shown in Figure 2;

Figure4 is a schematic diagram of a phase rotator for use with theapparatus shown in Figure 3;

FigureS is a schematicdiagram of-another form of aperiodicpolyharmonicgenerator, according to the'invent'ion, 'for use withtheapparatus shown in Figure 2;

"Figure lSis a table oflocal signal sources for outphasing unwantedharmonics which may be generated by the square law amplifiers ofthepolyharmonic generator asshown in Figure Figure? is a chartillustrating thevolume percentages of the component frequencies in whichis comprised the recognition of the character of a givenmusical'ins't'rumerit as exemplified by the percentages comprising onenote of the oboe;

Figure 8 is a schematic diagram of a dual sound-track magnetic recordercombination, according to the invention;

Figure 9 is a schematic diagram of a repetitious multisound-trackmagnetic recorder combination, according to the invention;

Figure 1013 a schematic diagram of anothr combinationof signalcontouring elements, according to the invention for use with theapparatus shown in Figure 2;and

Figure '11 is a schematic diagram of another combination'o'f signalcontouring elements, according to the invention, for use with'theapparatus shown in 'Figure2..

As shown in'Figure 1 apparatus according to the inventioncan be arrangedon;ajtable 1fin a convenient manner for use by a jcomp oser 2 located ata conven'ient height for operation ofthe apparatus by the composerseated before it. An audio oscillator 3, a polyharmonic generator 4 anda master switc board 5 are located on a shelf 6 runningacross theba'clco f the table. 1. Another shelf 7 supports on auditioningloudsp'eaker 8. located magnetic recording elcments as showncomprised 'l Pjhe&d' 1 t g. ad 0.- esol hea 11. me netic film 12,driving sprocket driving sprockets 14, "'15,;. carrying a film type ofsynchronoils one sheet 16. Projecting through the .top of the table at aconvenient working angle is an oscilloscope 11 fitted with a guide slot18 for atran slucent sheet 19011 which 'an opaque "envelope-conture lois. disposed. A fluorescent image 21 of an ultrasonic signal is shown hehind 191' A photocell 22in a hinged light-excluding cover ZIqmay-bepulled downby the knob 24 to, photoelectr'ically pi'clc up theinterrupted pulses 'of light caused V The table 1 hasit's op" On the topof the table 1 are 13. coupled to. j'which are by the contour line 20covering the travelling spot comprising. the, image. 21. may beassembled in recorded form by: Adjusting the audio oscillator 3 to afrequency corresponding to a fun damental of a note in a music score. Byinjecting the selected frequency into the polyharmonic generator 4, thecharacteristics of a desired musical instrument may be heard byadjusting the amplitude controls of the specified harmonics 25 which aregenerated in 4, and auditioning the combined output thereof by speaker 8as switched on at master control means 5.

A desired rendition of a singlenote is then. prepared by drawing anenvelope contour 20 'on 'the 'transparent sheet 19 using forexample agreasepencil. By closing cover 23 the photocell 22 will transmit thecontour every time the sweep repetition occursi Th control signal imageas modified by the contour 20 is biased ofl however by the single sweepadjustment of the oscilloscope. A push button control at 5 initiatesthesweep action forsingle horizontal scan of the contour according to.

the sweep time-constant selected. Each time the auditioning buttoninitiates the oscilloscope sweeping at the selected duration the outputfrom polyharmonic generator 4 will be partly transmitted to the speaker8 in accordance with the envelope 20 pulses 21 from the oscilloscope 17.By reshaping the attack and decay contours of the envelope 20 musicalnotes maybe edited as auditioned When a satisfactory note has beenproduced it may be recorded on magneticfilm 12 as often as it mayberequired in the score. By switching to automatic record at masterswitching control 5, the recording of the note occurring in preciseadvent placement may be arranged according to convenient cue marksindicated at arrow 26 by prerecording sweep track facility provided forthis purpose.

Further notes may be prepared in a similar fashion and'may be recordedonthe same track in staggered'or overlapping. placements as desired byplayback of'the recording at 9 and concurrently rerecording at 11 inmixed form with an additional seriesof placements of a new note. At thesame time if desired the recording which is picked up at 9 may be erasedat 10. In addition'the mixed recording and rerecording facilities byvirtue of theftr'ansverse multitrack capacity of the head arrangements9, 10, and 11 enable concurrent auditioning of notes in" the preparationof chords.

A, block diagram of the apparatus shownin Figure l. is giveninFigure 2.As shown in Figure. 2, the audio oscillator 3 feeds .the polyharmonicgenerator 4, which willbe described in more detail later. tours whichmay be based on the fimbrillated outlines of'oscillograms of notes ofmusic are inscribed at 20 on thesheet19. The sheet is disposed to coverthe luminous image 21. which is displayed on the cathode ray t ub e 17and which'is derived from. an ultrasonic oscillator 27 by connection tothe horizontal! 28 of the oscilloscope deflection system 30. 'Thevertical deflection plate isys tern 31of theo'scilloscope is connectedto 32: pulses from a sweep initiating which may be set to recordrecorder 33 at record head 34. Playback from head 34 may be routed byswitch 32 to fire the single sweep system. of the oscilloscope. Theswitch 32 may further connect oscillator 27 to the head 34 Manualfiring'of the single s push. button 35. The time base control of. thesingle sweep system of the oscilloscope is conventional electronicpractice and is not shown in order to reduce schematic congestion. Therecording of the single sweep firing signal is advantageously. combinedingof a sweep-duration controlling signal having an amplitude adjustedto provide in playback a biasing volt age for the grid of a tubeconnected to function as the variable resistance whichdetermines thetime constant of the capacitor associated with the oscilloscope swecp:

According to the invention music.

initiating .pulses on a special sound The envelope con for erasepurposes.v Veeps may be efiected .by.

with the record i magma system as aforementioned. Thus the adventplacement and the time during which a given contour envelope will beextended may be prerecorded. The range of the single sweep is made to beaproximately 0.1 to seconds duration for average musical synthesis.

The preferred electronic arrangement for the pickup of the contoursinscribed next to the face of the oscilloscope tube may be replaced bythe direct electrostatic sampling of the moving spot by using aconductive material for the contour line as inscribed, the inception ofthe line being connected to an electronic switch which in turn controlsthe variable transmission element 37. The use of the photocell (photomultiplier) pickup of the contour as shown in Figure 2 is preferredbecause more precise contour sampling is facilitated.

The envelope contour may be drawn on the surface of a translucent sheet19 or the contour may be an opaque cutout, and held in the guide slot 18between the photocell 22 and the cathode ray tube 28 at location' 29.The signal from photocell 22 may be connected by switch 36 to controlthe variable transmission element 37 which may be separately controlledby contour signals from 38 by switch 39. A source of audio as picked upby microphone 40 and amplified by 41 may be routed to an envelopedemodulator 38 by switch 42. Alternatively switch 42 may route the audiosignal to the electronic gain control element 43 which is connected inthe input of the polyharmonic generator 4.

The output of the variable transmission element 37 is connected to avolume mixer 44 to which is further connected playback signals from head9. The mixed pair of signals are connected to the recorder amplifier 45,the output of which may be routed by switch 46 to record at head 11 orthe output may be routed by switch 47 to control the variabletransmission element 37 with prerecorded contour signals.

A magnetic recording medium is preferred which may be magnetic film 12conventionally driven in the direction shown by the motor 48 asdetermined by the forward and reverse type motor control 49.

The erase head 10 is powered from oscillator 27 by switch 50. The switch51 is independent of 50 and supplies the signal for the control image21. Switch 52 provides means for rerecording with superposed envelopecontours by connecting the audio playback to amplifier 41 through 42 togain control 43 and a reprocessing operation as described.

All switches as numbered heretofor and additional switching routes (notshown), as will be described or postulated, are located for conveniencein the master switchboard 5 (Figures 1 and 2). To avoid overlycongesting the diagram, many of the connections to and from theswitchboard 5 are not shown, but are located in the direct routes asshown in the diagram.

The auditioning speaker 8 and amplifier 53 may be connected by switch 54to any signal in the system.

Referring now to Figure 3 which details one form of.

polyharmonic generator 4 as shown in Figures 1 and 2. The preferredgenerator is an aperiodic type. The usual method of harmonic generationselects, by resonant networks in the output of a non-linear transmissionelement, those frequencies which comprise 'the desired harmonic. Such amethod, however, will only perform part of the desired objectives ofthis invention as the harmonics selected will require readjustment ofthe resonant networks involved whenever the fundamental frequency ischanged. In the forthcoming disclosures it will be apparent that suchmanual tuning-in of multiple harmonics which may be shifting isinfeasible.

In Figure 3 the wave of the desired fundamental pitch as injected intothe electronic gain control 43, is fed to the input of an aperiodicquadrature amplifier 55 of novel design wherein multiple phase shiftsproduce the output on connection 56 and produce the output on connection57 each of which differs from the other by a constant phase rotation ofapproximately degrees over the audio frequency range. It is furtherunderstood that the pair of signals which are in quadratureat the:

output bear no fixed phase relationship to the frequency which maycomprise the input. She signals on 56 and 57 are injected into phaseinverter amplifiers 58 and 59. The four-phase outputs resultingtherefrom are quadrature fed to a virtual potentiometric ring or ringsas shown enclosed in the circle 60. It will be apparent to those versedin electronics that any desired number of polyphase voltage signalsources may be derived from connections made to the resistors comprisingthe rings as' schematized. Table 61 which is included in Figure 3, showsthe value of each resistance-segment in degrees around thepotentiometric ring multiplied by a suitable constant. In the schematicview a three-phase connection is shown, it being understood that anydesired number of phases may be connected to the appropriate taps in asimilar manner. In the three-phase example the connections feed therectifier array 62, 63 and 64 which are decoupled from cross-loadingeffects by resistors 65, 66 and 67. The output 68 in pulsating D. C. isinjected into a suitable square law amplifier 69 which is biased toproduce the third harmonic wave 70 of the injected input to theelectronic gain control 43 by means of nonlinear amplification of thehigher order harmonics otherwise produced as dotted in at 71. The volumecontrol 72 feeding the output 73 is decoupled from similar networks andgain controls from each of the other harmonics by means of resistor 74.The actual number of polyphase rectifier networks equals the number ofharmonics required of which ten have been found desirable.' A rectifieris required for each frequency which is involved in addition to thefundamental. In the case of a generator producing ten harmonics it isnecessary to use a total of 54 rectifiers.

Referring to Figure 4, which is a schematic view detailing one form ofthe aperiodic quadrature amplifier 55 shown in the circuit of Figure 3,the input signal is fed into two or more staggered phase-shiftingamplifiers at 75 I and 76. Each consecutive network 77, 78 and 79 in thecascade shown provides a degree maximum rotation of phase with changingfrequency. The phase-shifting constants are chosen to moderately overlapthe maximum rotation of a stage with the start of rotation of the nextstage at a given frequency. In the case of the three cascaded stagesshown a total output rotation of approximately 420 degrees relative tothe input may be obtained with a frequency range of 30 cycles to 10 kc.In a similar manner the cascade 80, 81, and 82 is designed to lag thecascade 77, 78, and 79 by a phase angle of 90 degrees over the audiofrequency band desired.

Another aperiodic means of generating polyharmonics is schematicallydrawn in Figure 5 wherein the input from the selected frequency isbrought to a constant amplitude by an electronic gain control 83 and isinjected into one of two species of square law amplifiers 84 and 85. Asis well understood in the electronic arts, the output will contain boththe input frequency and its first harmonic at connection 86. The inputfrequency also feeds a cathode follower output stage 87 whose output iscontrolled by potentiometer 88 and connected by a decoupling resistor 89to an output terminal 90 which is common to all harmonics. The output 86of the square law amplifier is fed to a cathode-coupled stage 91 througha resistor 92. The output 86 contains the amplified input frequency inopposite phase in and it is outphased in resistor 92 by means of a feedin from the cathode of stage 87 through an outphasing feed resistor 93.The remaining frequency 2 n is a desired harmonic and is controlled atcathode-coupled stage 91 by potentiometer 94 for injection into thecommon output 90.

The two output frequencies fn and 2fn which occur at the cathodes ofstages 87 and 91 respectively are de-- 7- square lawsarnplifier 85. As.is well understood in the art, thmoutput produced .by the resulting,-hetrodyne. is .com-.

prised of frequencies fn, 2m, 3131, and 47%.. The. fre-.

quency 3f); is fed to a,3r.d harmonic output stage 97 while the unwantedfrequencies fn, 2f anddfnare outphascd through resistor 98, 99;and lilO.The frequency 4 requiredfor outphasing is taken from stage 101 which isderived from the outphased output 162 of stage 1il3;while. the. otherfrequencies are outphased from thecathodes.

aretabled in Figure 6. It, will beapparent therefrom that outphasingfrequencies, as required for .the odd number harmonics, depend oncombinations wherein higher-frequency even number, harmonics areconcurrently produced.- It will further be apparent that electronicaperiodic harmonic generation, methods are disclosed whereby optionalharmonics may be forthcoming whereas the initiating fundamentalfrequency may be independently controlled orideletcd-a desirablefunction in the fullsynthesis of sound andmusic.

Referring again to Figure 2, the following is a description of a mode ofthe operations which may be used in theproduction of music according tothe invention:

Theconventional magnetic film 12 is threaded to feed from sprocket reel13. The record switch 46 is open. Cuesheets are prepared from thedesired musical score. Eachmusical note is deliberated and those whichhave the same pitch and which postulate similar execution from one giyeninstrument are transcribed. Notations of timir g advents which may. bederived from tables relating.

sound-track time lengths to conventional musical scoring are append x}:The notes listed are then marked on the film 12 in correct adventrelation by using a grease pencil orthe like. The film is stopped ateach position of the said marks, individual sweep-firing signals fromswitch Skate magnetically imposed thereon at head 34 and the film isreturned to the start position. Thereupon the oscillator 3 is adjustedby the aid of a chart which correlates electronic frequencies with musicnotations and the selected pitch is auditioned at speaker 8. The volumecontrols of the polyharmonic injector 4 are adjusted to inject thevarious harmonics required. The amplitudes of the yarious harmonicswhich,as in the case of the oboe, may be stronger than the fundamental,are provided in chart form as exemplified in the percentages shown inFigure 7. The sustainedcomplcx wave which is put out froimthepolyharmonic generator 4, as controlled by the percentage,settings,becomes subject to atransmission loss provided inthe variabletransmission element 37 Whichis controlled by the operating potentialsfrom the photocell 22 Referring to the oscilloscope display at 21, thevariable transmission element 37 will tend to integrate thellpulses and.be conductive in the rectangular display region .below the contour 20and will switch on deletingv or. blanking potentials whenever the spotleavesthis region and is above the envelope contour drawing Zi). Therate at which the switching occurs is determined by the ultra sonicoscillator frequency from 27. The length of time during which thecontour-controlled switching operation will lastis determined by theselection of. the single sweep time-basein the oscilloscope provided.In. this way the time-b seldetermincs the .duration in which the note ortouch ofmusic is sounding. Integration of the .varying switching pulsesin element 37 is provided exponentially according to well knownelectronic practice. Single sweep scanning of the envelope is initiatedby push button control 35 and in thismanner the combined complex tonefrom 3 and, 4 is prepared and can be auditioned. at speaker outputit.The grease pencil outline of the envelopercontour. Ztlmay be'modified byerasures until the musical; note has the precise qualities which aredesired.- The/correct recording volume 'level is obtained by ad--justment .of the mixer control 44.

and the single sweep switch 32 is. turned to automatic con: trol byusingthe firing. signal from 34,. Arccording-is. then made wherein theprerecorded advent signals onthe film edge ensure the precise envelopeplacemeutofeach repetition in the scorelof the note which hasbeen thustailored.

Additional frequencies of the same.,touch. and. char acter may beproduced by. simple adjustment of theaudio. oscillator The previousrecord, of sweepfiring signals may be erased by switching in, theoscillator 27 atswitchi 32 and anew note-timing advent-recording madeThc incoming recording from the variable transmission element 37 isauditioned in mixed-44formatwiththe playback signal from head 9.; Iffound satisfactory, it is. rerccorded on the same track by head 11-concurrently with .an. in-, tervening erasure at head), virtuallyaccomplishing the superposition of anadditional. recording.v It .will beapr. parent that the numberof rcrecordiugsemployed before undue lossfrom noise destroys the dynamic range .may. be limited. Therefore, thenumber of notes, of different pitch which may be prepared by the modeoutlined will belikewise limited. Amodification of the above mode may befollowed wherein all non-concurrent notes which:

are tohave the same harmonic structureand the .same envelope are groupedby each of the pitches prescribed, in the score. The required adventtimes are, pencil. marked on the film and followed by, the reeojrding34of all sweep-firing signals. The-magneticfilm isposi tioned to theadventmarks, and is backset. to iucludean, acceleration footage. The audiooscillator 3 signal at each pitch which is required is recordedfor atime which; is longer than the intended lengths of thefinal notes.- In,this manner, anumber of fundamental tones may be.-re, corded therebyreducing the number of rerecording operations, On playback, thesevarious sustained recorded tones areswitchedSZ to feed thepolyharmoniegenerator 4 through fll, 42, and 4.3 and are enclosed in theprepared sound envelope contour as outlined. The timing,adventsignalsinitiate the whole serics of envelope decayperiods of one typeused inthe score thereby rerecording notes of different frequencies on the sametrack in. one operation.

In the synthesis of notes ofcertain instruments such as the piano, wheretones concurrently sound on three, strings, an enharmonic structurewhich issiniilarmaybe obtained While performing the rerecording. Thismaybe accomplished .by concurrently connecting the demodulator 38(connection notshow n with a very low frequency from the audio,oscillator. switch 39 beingclosed. The re; sulting low frequencyamplitude modulation produces dif-.. ference frequencies with eachofthelfrequencies mime. complex envelope-enclosed noteslwhichiare beingrere corded. Other enharmonic efiects can be obtained byintroducing thesaid I amplitude modulation at theitime the recording lot the sustainedfundamentals are made;

Authentic; triple string effeets are obtained byprerecordingthreecomplex frequencies in superposition each..fre-.. quency-beingdisplaccdby a smalldifference from the previous one, recorded. The,triplerecordings -of.sus-. tained strings are located coveringeachposition where notes are to appear. The single sweep-firing signalsare recorded and the prerecordings of the sustained notes are playedback through the variable transmission elementwhich deIetesthcnr downtoenclosure in a given piano touch envelope to bc rerecorded again inthe manner' described.

Referring now to Figure 8 which is a schematic VI-CV? of a modificationof a portion of the recording arrangements diagrammed in Figure 2, asimple duplicationv of the playback erase and recordmagnetic headsandass'oci ated switches is shown. The advantages of this modi fi c tionwill be vapparent in that all/the aforementioned s thetic recordingoperations may be duplicated onjeach track and triple mixing operationsperformed. Synthesis The .output. of thc recording amplificrs45 isturned'to record, by. switch ,46;

of chords may be achieved and multiple instrument recordings prepared.While magnetic film 12 is shown, the use of magnetic tape for a twintrack system would be preferred. When magnetic film is used, however,multiple tracks may be recorded by utilizing heads 105, 106 and 107having transverse position-ability and the delimitation of the methodthereby is very complete.

A further advantage may be obtained by making successive superposedrecordings without intervening erasing operations. In this case therecording apparatus is adapted to enable the following novel method ofdualtrack recording to be utilized:

In Figure 8 postulate that a sequence of notes has been recorded on bothtracks, it being desirable to superpose a secondary sequence ofoverlapping notes thereon. To effect this without the recorder A. C.bias current partly erasing and distorting the existing recording, head107 is reconnected in lieu of head 105 and the volume of the resultingrerecording which is possible at head 11 is adjusted to neither add nordetract from the recording which exists on the track under head 11, theerase control 108 being turned off.

During this operation the aforementioned secondary sequence of notes maybe introduced through the variable transmission element 37 and asuperposed recording of the same added to the track under head 11. Therecording system connections are thereupon switched to enable head 11 topick up the superposed mixed recording which has been made to record thesame in a similar manner on the track under record head 107. No signalis introduced through the variable transmission element 37 in this stepwhich is a transfer step to enable both tracks to have the same record.This novel operation is introduced to enable the history of thesuccessive polarization positions of the particles on the recordingmedium which comprise the prior recordings, appropriately to modify theoperating center of the A. C. bias signal of recorder so that theincoming additional recording may include the aforementioned magnetichistory.

Referring now to Figure 9, the advantages of the method of thisinvention are further greatly enhanced by the multiple magnetic taperepetition recording arrangement shown. The pressure idler 110, which isreleasable, enables the concurrent driving of the multiple loops ofmagnetic tape in the direction of the arrow 111. The loop-driving motor112 may be separate from the main recording motor drive of the system.The magnetic heads 113 may act in playback, recording, and erasingfunctions. The associated connections and switchings which are not shownare well known in recording practice. The predominant value of themultiple loop arrangement centers in the feasibility of prerecording anumber of prepared notes of any kind, the whole or any part of the samebeing auditionable in parallel while the individual onsets of each notemay be manually repositioned by moving the relative position of theappropriate loop. Further advantage in the method accrues from the factthat part orchestrations or chords may be auditioned in whole while anundesirable component may be disclosed by switching off the offendingtrack. It will be apparent that the above advantages may be alsoachieved in the modification diagrammed in Figure 8 by the use of anumber of heads wherein each head combines the functions of heads 105,106 and 107 thereby enabling the recording of a number of trackssubstantially as described in connection with Figure 9. The repetitivefeature of the recording loops may be achieved by consecutivelyswitching the recording motor into reversing the magnetic film 12.

In the mode and method of the invention the multipletrack multiple-headalternative to the heads 105, 106 and 107 is preferred and isillustrated in Figure 1. The further modification embodied in themulti-loop combination shown in Figure 9 is desirable where extremedeliberation and perfection of synthetic recordings is required.

Referring again to Figure 1 wherein multiple-track recording isenvisaged, the operation of the method may be 10 further described inthe mode whereby percussive struc tures in music may be prepared. Arecording is made of substantially high audio frequency. A secondrecording is made of a frequency which differs from the previous recordby a small number of cycles. The recordings should overlap by a marginin total footage which is to contain the percussives to be recorded. Thetwo frequencies are switched at 52 to playback through the demodulator38 as shown in Figure 2. The resulting low frequency output is fed by 39to control the variable transmission element 37. Concurrently the audiooscillator is set to furnish the fundamental frequency required and theprescribed harmonic percentages are enclosed by element 37 in theenvelope contour which is scanned when initiated by pulses from 34. Thecombination with the above low frequency modulations creates differencefrequencies as is well understood in electronic practice, the resultbeing an enharmonic ringing which may be recorded. To the arrangementsexisting when the envelope note is re corded two modifications are made;namely, the time-base which was used is reset to be substantially 10% ofits former value and the oscillator frequency is adjusted to a somewhathigher frequency. The full length envelope note is played back andrerecorded concurrently with the short, 10% envelope note so that bothhave identical advent times in the mixed rerecording thereof. Thepercussive effect which is produced may be controlled over a wide rangeby the selection of the impact pitch or complex wave contained in theshorter envelope.

A further mode of operation whereby tremolo effects of thefrequency-modulated type may be carired out consists in prerecording thefundamental frequency required so that the recording is longer than thefinal footage required-the playback thereof being amplitude-modulatedwith a low audio frequency and made to directly control the transmissionelement 37. The result is rerecorded on an adjacent track. The tworecordings are mixed and injected into the polyharmonic generator 4 atthe prescribed percentages. The resultant frequency-modulated waves areenclosed at transmission element 37 in the designed envelope andrerecorded on the assembly track in the locations which are prescribedby the advent record from head 34.

Tremolo effects of the amplitude-modulation type are.

achieved by prerecording all the fundamental pitches pre scribed,adjusting the audio oscillator to furnish the amplitude modulationfrequency to the variable transmissionelement 37, concurrently playingback the prerecorded notes and injecting the same into the prescribedsetup of harmonic and envelope structure, the resultant amplitudetypetremolo notes being rerecorded.

A further mode of operation consists in the use of envelopes of playingtouch which are characteristic of certain instruments as the trumpet,while the harmonic structure which is selected is characteristic of avery different class of instrument as a violin. The harmonic structuremay be varied while the envelope is being scanned. Recordings preparedin this manner cannot be obtained from any musical instrument madeheretofore and they are of great interest to producers of music.

Another mode of operation consists in the modification of sounds whichare derived from a microphone. According to the method, new envelopestructures maybe assigned and new harmonic adidtions may be injected.The envelopes enclosing the live sound source may be extracted in thedemodulator element 38 or by the recti' fication of a double-sidebandsuppressed-carrier ultrasonic control-signal, the resulting liveenvelopes being used to enclose totally new complex wave structures suchas that derivable from a sustained singing or speaking voice.

Another mode of operation consists in the audible playback of a priorrecording-whereby a singer may a'ccompany the same'ove'r a microphoneinput and be concu'r rently'rerecorded with the original voice or withany other 1 1 complex characteristicfrequencywhich may be set up on thepolyharmonicgenerator.

Afurther mode of operationaccording to the invention,

consistsudnerasing arecorclcdnsustained, frequency. to accord with thecontours ,whichare to be applied, the erasing being effected atrecording speedby electronic means. Referring to Figure, 2, theerasingcontouring sig-.. nalmay be obtained from the photocell output at-22which.

isconnected to the record amplifier 45, the bias oscillator 27; being.disconnected therefrom, therecord head .11 functioning as, an erasingelement. Alternatively the erasing contouring-signal may beobtained fromthe oscillator 27 beingmadesubject to variable transmission by feeding.the signal through element BTwhich is made-subject to. dele-.

tions'by the contouring-signal fromphotocell 22.- The variabletransmission element may be connected at thev controlsighalinput toaudio-signals which may be derived from prior recordings or from themicrophoneinput,

and the oscillator output residue from element 37 after. amplification,through 45 being ,used to delete the prereresidue of which aftercontouring is played. back through thedemodulator 38, the resultingaudio, being utilized for further recording or auditioning in: theconventional anure Referring now to Figure 10, a possible alternative tothephotoelcctric system of scanning of a drawing or outline of desiredenvelopes, ,as shown in Figure 2, by parts 17 p to 2 4 and 28 to-37inclusive, is the method of directly erasing a wide track of a recordingof the sustained. tone which has v been prepared. According to theinvention, the sustained. tone is prerecorded on a Wide. tape loop of amagneticmedium 114 by the wide-track magnetic head 115.v A maskingcut-011L116, or the mental equivalent is disposed on the stationary loop.as dotted at 11-7.- An A. C. or D. C. operated or magnetizederasetpcncil 118 is made to erase all the complex wave striations whichhave been recorded excepting only that region protected by themask ofthe required envelope of the desired note. The loop of recording residuewhich remains and which comprises the. desired note is rerecorded asoften as the note is prescribed to appear inthe synthetic record ofmusic which is being assembled. The main recording drive motor 48 inFigure 2 or an equivalent interlock or synchronous system is used M48.in Figure 10. A synchronous relationship is preferred as a means ofensuring thetransferof theprecise placement of the onset time of eachnote to be rerecorded. While this alternative arrangement of theelementsin the system will' enable the: method of the invention to be performed,it is not preq.

ferredin that an individual envelope shape is required for each. changein decay time or length of a given note.

A further alternative to the photoelectric scanning ofa drawing oroutline. of the desired envelopecontour is the arrangement shown. inFigure, ,11' which ,is. preferred over the arrangements of Figure 10, Itis not a preferred alternative to the photoelectric scanning of envelopedesigns,

Referring n w to F u ec as a sne q -s oscillator 120 isrccordedfor onerevolution of the magnetic loop 121 by means of the wide-track head 122. The

control signal recording, which otherwise provides a sustainedloutputrectified signal from an amplifienand re tifier 123 is modified manuallybymagnetic: erase-pencil deletions. The required envelope design may bea cu tout l 24 disposed to guide the activitiesof theerase pencil 118 onthe stationary recording. Precise ,positioning of the; onset is markedon thejtape' by grease pencil, said mark correspondingwith. the adventmarkonthhssembly recording film. The main recording drive motorisrelatedby drive tothe motion of the loop 121 by meansof thespeed-changer element 126 underspeed-reduction control 121. Thecombination of these elements enables a single designof envelope to beprecisely located as to the advent time of the envelope placement whilea wide, range of envelope duration times may be directly selectedthrough speed-reduction control 127. The erasure of the control signalrecording, wherever unmasked by the cut,-. out shape of the desiredenvelope, enables the variable gain transmission element 37 to transmitsubstantially the shape erased as in the control signal.

While the instantaneity of playback of magnetic recording systems is ofparticular advantage in the recording and,

rerecording assembly of the components of music according to theinvention, the operations may be performed, by means of suitablymodified disc recording elements.

In disc recording according to the invention the precise location andplacement of the various advent times of the noteswhich are beingrecorded may be achieved by pre-.

recording the prepared notes in a concentrically arranged series on asource disc suitably marked with peripheral indexing cues, andrerecording notes selected therefrom onto a synchronously interlockedsecond recording disc.

The musical notes which are to be prerecorded are pre--- pared accordingto the method and means which have been described in connection withFigures 1 and 2 using to perform the same operations by utilizing asingle turntable and recording channel in combination with two or moreplayback pickups and mixing means which feed the recording head forconcentrically related rerecording functions. In this case the indexeddisc of prerecorded notes as prepared is of larger diameter than thedisc which is to receive the assembled rerecordings of the notes. Thusthe smaller disc is superposed on the larger source disc which ismanually indexed in relation thereto in accord with the precise adventlocations of notes as indicated. Where overlapping notes in theproduction of chords, etc. are indicated the rerecording operationswill' involve alternation from the upper to the lower and outer discarea and vice-versa, the ease of positioning and exchange of the recordsbeing an advantage over other systems of recording.

In the case ofoptical methods of recording the method of the inventionmay be applied by utilizing a number of filmphonographs working insynchronous combination with a mixing and rerecording facility as iswell known in motion picture practice. With such facilitiesit isnecessary to make prior recording and processing of a film library ofsustained frequencies having every pitch and instrument characterizationas prescribed in the music score to be assembled. Appropriatefootages ofthese sustained tones are out together according to the necessary'spaced apart relationships as indicated in the music score, for allnotes which are to be in non-concurrent placement in the finalrecording. Additional reels of ap-, propriately spaced apart sustainedfrequency optical film footage are prepared for those parts of the musicscore which require overlapping notes. By fecdingthe filmphonographplayback signals from the reels tothe contou r deleting element andcombination as described in Figure 2, parts 17 to 37 inclusive, eachfrequency may be deleted to a residue of the appropriate touchas'determined by the contour pattern employed. The firing of the singlesweep scan is conveniently produced by connecting the playback signal tothe single-sweep firing circuit of the oscilloscope according to themode outlined in connection h Fi ur Another neans for thecontour-deleting operation ac: cording to the method of the inventionconsists in the application of opaque matter to the sound-tracks ofthe.

prepared reelsof selected sustained frequency recordings. The opaquematerial may be manually applied by pencil, brush or air-brush accordingto masks or templates of contours as determined by experience or bystudy of sound amplitude contours as exemplified in variable area motionpicture film recordings of mechanical musical instrument sounds.

A further means for the contour-deleting operation of the inventionconsists in the preparation of sound recordings of a control. frequencywhose amplitude is varied at the time of recording according to contourselectronically derived from noise-reduction signals which are producedin motion picture optical recordings, and which have been initiated bythe pickup of mechanical musical instrument sounds. The controlfrequency contours thus recorded are processed and collected in alibrary for convenience in the assembly of the aforementioned reels ofsustained frequencies in appropriate relationships as prescribed in thescore. In playback the sustained frequencies are connected to feedthrough a variable transmission element which is controlled by thesynchronous playback signals from the control frequency contour reeldescribed above. The resulting residue of the sustained frequencies isrerecorded in mixed relationship with additional concurrent playback ofthe overlapping sustained frequency reels and control frequency contourreels as required by the musical score in assembly. It will be apparentthat the operation of individual advent placement of control frequencycontours is manually effected at the time of the cutting together of thefilm reels in their preparation.

To enable the rerecording of the overlapping sounds on the reels whichhave been prepared as described, it is necessary to duplicate thedeleting element and combination as described for each concurrentlyoperable filmphonograph facility which is employed. The multiple outputsof the prepared residues from each of the reels involved are mixed atthe appropriate volume levels and rerecorded optically by means of astandard film sound recorder. The resulting recording is processed forplayback according to motion picture practice.

It is to be understood that the word recording as used in the appendedclaims refers to playable sound-tracks disposed on a suitable recordingmedium as exemplified in mechanical, magnetic or optical recordingsound-tracks on disc, tape, wire, or film.

What I claim is:

1. A method of producing sounds comprising the following steps,producing an audio frequency current, making an envelope contouraccording to a progression of instant amplitudes of sound, variablycontrolling said audio frequency current until the residue of said audiofrequency current conforms to the said envelope contour, and reproducingsaid residue.

2. A method of producing recorded sounds comprising the steps ofproducing an electric current corresponding to a sustained soundfrequency, making an envelope contour according to a progression ofinstant amplitudes of sound, deleting the amplitude of the currentcorresponding to the sustained sound frequency until the residueconforms to the envelope contour, recording said residue of the soundfrequency according to given advent placements on the sound-track of arecording.

3. A method as defined in claim 2, in which the step of producing asustained sound frequency is carried out by injecting a given frequencyinto an aperiodic polyharmonic generator, adjusting the amplitude of theinjected frequency, adjusting the amplitude of each of the harmonicfrequencies generated and combining the adjusted frequencies in a singleoutput.

4. A method as defined in claim 2, in which the step of producing asustained sound frequency includes producing specified and individuallyadjusted harmonics from any given frequency by the steps of rotationallydisplacing more than one phase therefrom, maintaining a constant phasedisplacement between the displaced phases by utilizing staggeredcascaded phase rotators and distributing the polyphase outputs producedaround an equipotentiometric ring of resistors, feeding the outputs fromindividual rectifier groups connected to appropriate polyphase points insaid ring of resistors to individual square law amplifiers, furtherfeeding the specified harmonic outputs resulting therefrom throughindividually adjusted volume controls to a combining output network.

5. A method as defined in claim 2, in which the step of producing asustained sound frequency includes producing specified and individuallyadjusted harmonics from any given frequency by injecting the givenfrequency into an array of square law amplifiers and adjusting theamplitudes of the various specified harmonic outputs therefrom, andutilizing the specified harmonics to outphase other output frequencieswhich may be concurrently generated.

6. A method as defined in claim 2, in which the step of deleting theamplitude of the current corresponding to the sustained sound frequencyis carried out by sending the said current through an electronicvariable transmission means subject to a control signal, scanning asingle sweep oscilloscope image of the said control signal byprotoelectric means, covering the oscilloscope display with a desiredopaque envelope contour disposed on a transparent surface and connectingthe modulated photoelectric control-signal output resulting therefrom tothe control terminal of the said variable transmission means.

7. A method as defined in claim 2, in which the step of deleting theamplitude of the current corresponding to the sustained sound frequencyis carried out by recording the said frequency on a wide sound-track,disposing an envelope contour guide upon said sound-track whilestationary, and obliterating a part of the recording of said frequencyuntil the residue conforms to the said contour guide.

8. A method as defined in claim 2, in which the step of deleting theamplitude of the current corresponding to the sustained sound frequencyis carried out by sending said current through a variable transmissionmeans subject to a control signal, recording the control signal on awide sound-track, disposing the envelope contour upon said sound-trackwhile stationary, obliterating the recorded control signal until therecorded control signal conforms to said envelope contour andcontrolling said transmission element by the resulting residue of therecorded control signal.

9. A method as defined in claim 8, in which the resulting residue of thesound frequency is recorded according to a given advent placement on thesound-track by synchronizably and identifiably relating it to the adventtime of the recorded control signal by interlocking the driving means ofsaid sound-track of said residue of the sound frequency and of the widesound-track of the control signal, feeding the output of the variabletransmission means through manual gain controlling means to the input ofthe recording means for said sound frequencies to be re corded andrecording said residue of the sound frequency according to a givenadvent and assembly placement on the sound-track by the further step ofplayback of the wide sound-track control signal.

10. A method as defined in claim 2, in which the sustained soundfrequency is recorded, and the step of deleting is carried out byobliterating the recorded sustained sound frequency to accord with theenvelope contour by superposing a recording on the recorded sustainedsound frequency.

11. A method as defined in claim 2, in which the sustained soundfrequency is recorded and in which the step of deleting is carried outby superposing an erasing frequency which has been modulated withsounds.

12. A method as defined in claim 2, in which the sounds produced arenotes in a musical arrangement and whichincludes: the step ofrecordingthe notes nonsequentially .according to deliberated advent placements;

13. Armethod as defined in claim 12, in which the steps of recording areperformed magnetically.

14.- A method as defined in claim 2, in which the step of making theenvelope contour is performed by electrically integrating a progressionof instant amplitudes of sound and by utilizing the integration soobtained to control a variable transmission means which is connected todelete the sustained frequency.

15. Amethod as defined in claim 14, in which thevariable,,transmissionelement is controlled by a carrier fre quencymodulated with the integration of the progression of instant amplitudesof sound.

16. A method of producing recorded sounds in which predetermined adventplacements of sound in the recordingon a first sound-track are obtained,comprising the steps of recording a sweep initiating signal on a secondsoundtrack at given advent points, the second sound-track beingsynchronously related to the first sound-track, using a playback signalfrom the second sound-track to initiate a-single sweep of the beam of anoscilloscope, connecting the oscilloscope to display a frequency imageof an oscillator output signal, superposing a given contour on saidimage, photoelectrically scanning a part of said image as defined bysaid contour, utilizing the photo-electric current to control a variabletransmission circuit, transmitting through said transmission circuitcurrents corresponding to sound waves and recording the resultingresidue of sound according to the recorded sweep initiating signals.

17. A method of recording notes in a musical arrangement. in: which thenotes are recorded nonsequentially comprising the steps of recording agiven sustained sound frequency on an endless sound-track, deleting therecording of said given sound sustained frequency according to aprogression of instant amplitudes of a secondary sound, rerecording theresidue of said recording and synchronizably and identifiably relatingthe advent placement thereof by interlocking the driving means of bothrecorders.

18. Apparatus for producing sounds comprising a source of currentscorresponding to sound waves, an electronic demodulator for formingcurrents corresponding to the envelope of the amplitude variations ofsaid sound waves, a source of sustained audio wave currents of givencomplexities, an electrically-controlled variable transmis sion meansconnected to transmitand adapted to delete said sustained audio wavecurrents according to said envelope and means for reproducing theresidue current output from said transmission means.

19. Apparatus as defined in claim. 18,-in which the source of currentscorrespondingto sound Waves is a microphone pickup.

29. Apparatus as defined in claim 18, in which the sourceof currentscorresponding to sound waves is a sound record operating a pickup head.I

21. Apparatus as defined in claim 18, in which the reproducing meansincludes sound'recording and playback elements. v

22. Apparatus as defined in claim 18, in which the source of sustainedaudio Waves comprises a source of currents corresponding to sound wavesin combination with constant amplitude maintaining means for sustainingsaid audio waves.

23. Apparatus as defined in claim 1B, in which the source of sustainedaudio waves is an audio oscillator in combination with a polyharmonicgenerator.

24. Apparatus for producing sounds comprising the combination of asource or" audio frequency currents, an electrically controlled variabletransmission means for varying the transn'iission of said audioirequency currents, at source of control currents for controlling saidvariable transmission means, a surface adapted to modify said controlcurrentsaccording to sound envelope contoursdisposed thereon and meansfor reproducing the residue of audio frequency current in the outputfrom said transmis,

sion element.

25. Apparatus as defined in claim 24, in which the surface is atransparency adapted to modify the luminous display from an oscilloscopefor displaying an image of said control currents, and which comprises aphotocell arranged to scan the modified luminous image and to have itscurrent output varied in accordance therewith, the variable transmissionelement being arranged to be controlled by said current output of thephotocell.

26. Apparatus as defined in claim 24, in which the surfaceadapted tomodify the control currents is a recording of said control currentsarranged so that the playback currents therefrom control the variabletransmission element.

27. Apparatus for producing sounds comprising a source or" audio wavesof given complexity, variable transmission. means for controllablytransmitting the said waves, a source of control current for controllingsaid variable transmission means, means for modifying said controlcurrent in accordance with photoelectrically scanned contours of givensound wave envelopes, means for initiating the photoelectrical. scanningof said contours according to recorded given advent signals, recordingmeans arranged to record the output currents of said variabletransmission means in synchronous relation with said recorded adventsignals.

28. Apparatus for producing recorded sounds comprising a source of audiowaves of given complexity, variable transmission means for. controllablytransmitting the said waves thercthrough, a source of control currentfor con trolling said variable transmission means, means forcapacitatively modifying said control current in accord- .nce with ascanned contour of a given sound wave envelope, means for initiating thescanning of said contour according to prerecorded given advent signals,recording means arranged to record the output current of said variabletransmission means in synchronous relation with said prerecorded adventsignals.

29. Apparatus for the generation of currents of given complexity from asource of current. of any given frequency comprising plural phaserotating networks having constant phase rotation relationshipstherebetweenconnected to produce polyphase rotation of currents in anequipotentiometric ring of resistors, progressive polyphase pointsthereon connected to individual rectifierelements having parallel outputcircuits connected to the input circuits of individual square lawamplifier tubes which are connected to manually operable volume controlmeans connected to a common output terminal.

30. Apparatus for producing recorded sounds compris-.

ing an electronic generator of sustained audio waves, a polyharmonicgenerator connected thereto, an electrically controllable variabletransmission means connected to the output of the polyharrnonicgenerator, a generator of a secondary frequency connected to a contourdetermining means which is connected to control said variabletransmission means, said variable transmission means being connected tosound recorder elements whichare adapted to automatically initiate thesaid amplitude controlling means to record according to predeterminedadvent positions on said recording.

31. Apparatus for producing two or more signals having essentiallyconstant desired. phase displacement relations to each otherthroughoutanextensivefrequency spectrum comprising, a source of signals within saidfrequency spectrum, a separate channel associated with each of thedesired phase displaced signals said channels being fed in parallel bysaid source of signals, said channels each comprising a series ofcascadedstages, the number of said cascaded stages preferably being ofthe order of at least one per decade of frequency spectrum; each of saidstages in each channel comprising, phase inverting means operablethroughout said frequency spectrum whereby equal output signalsdifi'ering in phase by degrees are provided between a reference phaseterminal and two output terminals, a phase shifting pair of impedancesconnected in series between said. two output terminals, the inputterminals of the succeeding stage in the channel being connected betweensaid reference phase terminal and the common junction point of said pairof impedances; the phase displacements of the said phase-shifting pairsof impedances of the stages in each channel being selected to providephase rotations progressively stage by stage throughout said frequencyspectrum, the phase displacement of each corresponding stage in the saidseparate channels being selected to provide phase displacement relativeto each other equal to the desired relative phase displacement betweenthe outputs of said channels.

32. An aperiodic polyharmonic generator comprising a source of signalsof fundamental frequency, an array of two species of square lawamplifiers, means to apply to the input of the first of said species ofamplifiers fundamental and odd harmonic signals as generated within thearray by the second species of said amplifiers, the output of said firstspecies of amplifiers containing double frequency components of theinput signal, means to apply to the input of the second of said speciesof amplifiers both double frequency signals as generated by said firstspecies of amplifiers together with odd harmonic signals, the output ofsaid second species of amplifiers containing sum and diiferencefrequency components of the input signals, and means to apply to theoutputs of both species of amplifiers out-phasing signals as presentwithin the array said out-phasing signals being arranged so as to cancelthe undesired frequencies present in said amplifier outputs.

References Cited in the file of this patent UNITED STATES PATENTS1,967,238 Goldthwaite July 24, 1934 1,967,239 Hardy July 24, 19342,144,337 Koch Jan. 17, 1939 2,203,353 Goldmark June 4, 1940 2,402,058Loughren June 11, 1946 2,462,263 Haynes Feb. 22, 1949 2,476,349 BeardJuly 19, 1949 2,511,121 Murphy June 13, 1950 2,528,709 Raymond et alNov, 7, 1950 2,532,803 Fauss Dec. 5, 1950 2,540,406 Ranger Feb. 6, 19512,546,850 Chancenotte Mar. 27, 1951 2,548,011 Frost Apr. 10, 19512,550,775 Clark May 1, 1951 2,559,505 Hillier July 3, 1951 2,563,647Hammond Aug. 7, 1951

